Local magnetic and electronic properties of the A2FeM'O6 (A = Ba, Sr, Ca, M' = Mo, Re) double perovskites

The results of a combined NMR, X-ray absorption spectroscopy and X-ray magnetic circular dichroism study of the AA'FeMoO6 and AA'FeReO6 double perovskites are presented. They revealed a dependence of electronic and magnetic properties, including a d-electron transfer between Fe and Mo sites, on the structural tolerance factor. The maximum value of the 4d Mo electron occupation and the corresponding Mo moment is obtained for the tolerance factor of unity. This corresponds to the maximum strength of the magnetic interaction and, respectively, to the Curie temperature. The dominant T-5/2 type temperature dependence of the Mo hyperfine field reveals the half-metallicity of the AA'FeMoO6 compounds. Antisite defects and antiphase boundaries have been identified in NMR measurements and the strength of their magnetic coupling have been determined. A considerable orbital contribution to the Re and Fe magnetic moments were found in the NMR and X-ray magnetic circular dichroism measurements on the AA'FeReO6 compounds. Its magnitude decreases with increasing structural tolerance factor and is correlated with their magnetic anisotropy.